Question

Describe how a web page is retrieved and viewed by a web user.

Short answer

A webpage is retrieved through URL entry, DNS resolution, connection establishment, HTTP request, and server response, before rendering by the browser.

Step-by-step solution

Entering a URL

The process begins when a user enters a Uniform Resource Locator (URL) into the web browser's address bar. A URL is an address that specifies the location of a web resource, such as a webpage. For example, typing 'www.example.com' into the browser tells the browser what you want to access.

DNS Resolution

After entering the URL, the browser sends a request to a Domain Name System (DNS) server to resolve the domain name into an IP address. This is because computers use IP addresses to identify each other on the network, so the domain name like 'example.com' needs to be translated into an IP address, such as '203.0.113.5'.

Establishing a Connection

Once the IP address is obtained, the browser requests to open a connection with the server hosting the web page. This is typically done via the Hypertext Transfer Protocol (HTTP) or its secure version (HTTPS). The browser and server establish a connection, often completing through a 'handshake' process especially in HTTPS to ensure security.

Sending an HTTP Request

With the connection established, the browser sends an HTTP request to the web server. This request includes methods, such as GET, to retrieve the webpage requested by the user. The server needs to understand this request to send back the correct data.

Server Processing and Response

The web server receives the HTTP request, processes it, and retrieves the webpage data. This data is typically structured in HTML, CSS, and JavaScript files. The server then sends this data back to the browser in the form of an HTTP response.

Rendering the Web Page

When the browser receives the HTTP response, it processes the HTML, CSS, and JavaScript to render the webpage visually. The HTML structures the content, CSS styles it, and JavaScript provides interactive elements. This entire process allows users to view and interact with the webpage in their browser.

Key concepts

DNS Resolution

DNS Resolution is the key step in transforming a human-friendly domain name into a computer-friendly IP address. When you type a web address into your browser and press enter, a request is sent to the Domain Name System (DNS). The purpose of the DNS is to locate and translate a domain name like \( www.example.com \) into a numerical address such as \( 203.0.113.5 \). This numerical address is known as the IP address, which computers use to locate and communicate with each other over the internet.

The process usually involves several DNS servers. Here's a simple breakdown:

• Your browser first checks its own cache for the IP address of the requested site.
• If not found, it queries the local DNS server provided by your Internet Service Provider (ISP).
• If the local server doesn't know, the request is escalated up to a higher-level DNS server until an authoritative DNS server is contacted.
• Finally, the domain name is resolved into an IP address, which is then used to communicate with the targeted web server.

This entire translation is vital because IP addresses are required for routing information over the internet.

HTTP Request and Response

After obtaining the IP address through DNS Resolution, the web browser initiates an HTTP Request to connect with the web server. This request involves using the Hypertext Transfer Protocol (HTTP) or its secure version, HTTPS, to retrieve the desired web page data.

This process works as follows:

• The browser sends an HTTP request message to the server. Common request methods include GET, which requests data from the server, and POST, which submits data to the server.
• The server receives this message and processes it to understand what resource is being requested.
• The server then crafts an HTTP response which includes the status code (such as 200 OK), headers containing information about the data, and the requested webpage content itself.

In HTTP's secure variant (HTTPS), this communication is encrypted to protect user data and privacy.
HTTP Request and Response are fundamental for transmitting data across the web, enabling browsers to fetch and display the web content you need.

Web Browser Rendering

Once the browser receives the HTTP response from the server, it begins the complex task of rendering. Rendering is the process of interpreting the data like HTML, CSS, and JavaScript to visually display the webpage.

Here’s how it works:

• The browser parses the HTML to construct the Document Object Model (DOM) tree, which is the page's structure.
• CSS is then applied to style this structure, determining layout, colors, fonts, and spacing.
• JavaScript, if present, is executed to add interactive elements such as animations or user-triggered events.

The rendering engine in browsers works tirelessly to ensure all visual elements are displayed promptly and correctly. It optimizes the process by doing things like laying out the text before all images and advertisements fully load, so users can start reading without delay.
This process makes web pages interactive and visually appealing, allowing users to engage with the content effectively.

IP Address Translation

IP Address Translation is an essential under-the-hood process in web page retrieval. It refers to the conversion and communication of the network address given in the request process. After DNS Resolution provides the IP address, other systems, known as routers or gateways, can also perform translation if needed.

This typically involves:

• Network Address Translation (NAT) where routers modify network address information in IP headers of packets when they pass through a router.
• This allows for the mapping of multiple local private addresses to a single public IP address before information is transmitted over the internet.
• By using NAT, organizations efficiently manage IP address space, often conserving public IP addresses.

IP Address Translation ensures that data packets are directed correctly to their intended destinations, bridging networks securely and allowing seamless internet connectivity.